Economic impact of an epizootic of pseudorabies in a commercial swine herd in Ohio, achieving test negative status and quarantine release by use of vaccination and test and removal.

The effect of pseudorabies in a commercial farrow-to-finish operation on selected production and economic values was estimated. Pseudorabies was first diagnosed in this herd by circle testing done in March 1988, as a required part of follow up from another herd that had been diagnosed with pseudorabies in the area. A pseudorabies virus vaccination program was initiated in the herd at that time. The mean litter size of pigs born alive varied from 9.26 to 10.02 pigs/litter throughout the study period; however, there was a twofold increase in suckling pig mortality and a 2.6-fold increase in nursery pig mortality when the months of the epizootic were compared with pre-epizootic months. In the 6-month period following the epizootic, suckling pig mortality was three-fold higher than that reported in the preepizootic months. Total net loss for this operation was estimated at $99,700 from when the epizootic started until eradication, when calculating losses directly. The major economic losses (76.5% of total loss) were related to suckling pig mortality, which was $16,240 during the epizootic or $24/inventoried sow/week; $19,395 in the 6 months following the epizootic or $3.8/inventoried sow/week; and $40,628 thereafter until eradication 26 months later or $0.37/inventoried sow/week. Nursery pig mortality losses were 12.6% of total net losses; $754 during the epizootic, $357 in the 6 months after the enzootic, and $11,444 thereafter until eradication 26 months later. Sow culling and deaths accounted for 9.4% of net losses that took place from 6 months after the epizootic until eradication.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mathematical model for the impact of a pseudorabies epizootic on the productivity of a farrow-to-finish operation

A fully age-structured deterministic model of the population biology of a pseudorabies epizootic in a farrow-to-finish operation was used to examine the disease-related change in productivity following the initial disease episode. A strategy involving continual sow vaccination was compared with various strategies involving the vaccination of growing pigs, as well as sows. The model suggests that vaccinating growing pigs, in addition to the breeding herd, results in only a relatively small improvement in long-term productivity following a pseudorabies epizootic.     

Prevalence of pseudorabies virus infection and associated infections in six large swine herds in Illinois.

Sera were collected from 6 large farrow-to-finish swine herds infected with pseudorabies virus (PRV) in Illinois. All herds were participating in the Large Herd Cleanup Study, a USDA-initiated project to evaluate the feasibility of eradicating pseudorabies from large farms (greater than 400 sows) by use of a combination of vaccination and management changes. Herd size ranged between 425 and 1,500 breeding females. Between April and July 1990, sera for measurement of PRV antibodies were obtained from 113 to 156 sows and 112 to 162 finishing pigs (body weight greater than 70 kg)/herd. Duplicate sera from 30 sows and 30 market-weight pigs/herd were obtained for measurement of serum antibodies to the following associated organisms: swine influenza virus, transmissible gastroenteritis virus, encephalomyocarditis virus, Actinobacillus pleuropneumoniae, Eperythrozoon suis, and 6 serovars of Leptospira interrogans. Prevalence of PRV antibodies attributable to field virus infection ranged between 53.8 and 100% for sows and between 0.7 and 97.3% for finishing pigs, as determined by the appropriate differential test for the vaccine being used on each farm. In only 1 herd, PRV seroprevalence was increased with higher sow parity. For associated infections, the risk of seropositivity attributable to PRV was not significant (for most infections) on all farms and varied among farms. Thus, pseudorabies did not appear, in general, to increase susceptibility to infection with other disease agents.     

Financial impact of transmissible gastroenteritis in pigs

The financial impact of an epizootic of transmissible gastroenteritis in pigs was evaluated in a California sow herd through estimating growth, feed, and profit functions. Two groups of pigs were studied: pigs born before and surviving the epizootic (epizootic [E] pigs), and pigs born after the epizootic (postepizootic [PE] pigs). Short-term profits were maximized at 165 days for both groups of pigs, ranging from $47.14 for female E pigs to $60.32 for male PE pigs. Accordingly, it was concluded that pigs surviving or born shortly after a transmissible gastroenteritis epizootic are profitable to raise, if raised under management conditions similar to those in the study herd.     

Isolation of swine infertility and respiratory syndrome virus (isolate ATCC VR-2332) in North America and experimental reproduction of the disease in gnotobiotic pigs.

A recent epizootic of swine infertility and respiratory syndrome (SIRS) in a Minnesota swine herd was investigated. Examination of a sow, neonatal piglets, and stillborn fetuses obtained during the epizootic from the affected herd revealed interstitial pneumonitis, lymphomononuclear encephalitis, and lymphomononuclear myocarditis in the piglets and focal vasculitis in the brain of the sow. Fetuses did not have microscopic lesions. No cause for the infertility and respiratory syndrome was determined. Therefore, attempts were made to experimentally reproduce the disease. Eleven 3-day-old gnotobiotic piglets exposed intranasally to tissue homogenates of piglets from the epizootic became inappetent and febrile by 2-4 days postexposure and had interstitial pneumonitis and encephalitis similar to that seen in the field outbreak. After 2 blind passages in gnotobiotic piglets, tissue homogenates were cultured on continuous cell line CL2621, and a cytopathic virus (ATCC VR-2332), provisionally named SIRS virus, was isolated. Gnotobiotic piglets exposed intranasally to the SIRS virus developed clinical signs and microscopic lesions that were the same as those in piglets exposed to the tissue homogenates, and the virus was reisolated from their lungs. This is the first isolate of SIRS virus in the United States that fulfills Koch's postulates in producing the respiratory form of the disease in gnotobiotic piglets and the first report of isolation and propagation of the virus on a continuous cell line (CL2621). The virus is designated as American Type Culture Collection VR-2332.     

The shedding of group A rotavirus antigen in a newly established closed specific pathogen-free swine herd.

A longitudinal study was undertaken in a newly established specific pathogen-free (SPF) swine herd to determine the dynamics of rotavirus antigen shedding in a closed swine facility. Pregnant SPF gilts which populated the herd, and their offspring, were monitored weekly for three consecutive lactations. Fecal samples were assayed for the presence of group-specific viral antigen by a solid phase immunoassay (ELISA). Results indicate that in the week prior to farrow, 35% of samples from gilts/sows contained rotavirus antigen. During nursing, 37% of the gilts'/sows' fecal samples also contained virus antigen. Over the course of three farrowings, every gilt/sow in the herd excreted virus antigen. Virus antigen was present in 25% of the samples tested from nursing pigs and in 70% of the samples tested from pigs in the postnursing period; 95% of the litters excreted virus antigen either while nursing or postweaning. Seasonal incidence in virus antigen excretion was noted with proportionally more suckling pigs virus antigen-positive in summer and proportionally more sows/gilts positive during winter. Diarrhea occurred only rarely in the sampled population. Although piglets shed rotavirus subclinically, ELISA positive feces from piglets of each lactation caused severe disease when fed to neonatal gnotobiotic pigs. Electropherotyping of these passaged viruses indicated minor variation in RNA banding patterns over time.     

Variation of Aujeszky's disease viruses in wild swine in USA

In the United States of America, Aujeszky's disease (pseudorabies) has been eradicated from all domestic swine. Some re-emergence of infection occurred as vaccine use diminished. Sporadic outbreaks have also occurred because of the reservoir of infection in feral swine that have spread across the southern two-thirds of the country and Hawaii. In order to be able to understand the origins of re-emerging virus, sequence analysis of variable genes in pseudorabies virus (PRV) has been used to differentiate strains. Most PRV from feral swine can be distinguished from virus circulating in domestic pigs during the national epizootic. However, several feral swine isolates of PRV from south central states are closely related or identical in sequence to strains from domestic pigs. Extensive study by PCR for the presence of virus in the oral cavity of feral pigs disclosed that the viral DNA is distributed widely in tonsils salivary glands, taste buds and even mucosa in the vicinity of tusks. Clearly the virus in feral swine has multiple mechanisms of transmission to insure persistent infection and the threat of re-emergence in domestic swine continues.     

Factors associated with circulation of pseudorabies virus within swine herds

Data were collected from 104 Minnesota swine farms quarantined for pseudorabies virus (PRV) infection. Each herd was serologically evaluated for the presence of antibodies to PRV in finishing pigs. Herd management practices, swine housing design, and disease profiles were described for each farm. Multiple logistic regression analysis was used to determine which factors were associated with circulation of PRV in the finishing pigs of farrow-to-finish farms. Sixty-seven (64%) of the herds had no serologic evidence of PRV circulation in the finishing section, whereas 37 herds (36%) contained at least one PRV seropositive finishing pig. The odds of a given finishing herd being seropositive for PRV were 2.85 times higher if the finishing pigs were housed in confinement (P = 0.01), 2 times higher if Actinobacillus (Haemophilus) pleuropneumoniae was a clinical problem in the herd (P = 0.03), 1.36 times less for each year that passed since the herd quarantine was issued (P = 0.01), 1.74 times higher if clinical signs of PRV were reported (P = 0.04), and 1.52 times higher if animal protein was included in at least one of the rations (P = 0.08).     

Epizootic of pseudorabies among ten swine herds.

An epizootic of pseudorabies in 10 swine herds located near Greensburg in Decatur County, Indiana was investigated. Records of Decatur County swine herds previously quarantined because of pseudorabies were obtained. For the 1988 epizootic, clinical findings were considered, location of each of the 10 swine herds in relation to the other herds was determined, and potential fomites were considered. Meteorologic data prior to, during, and after the epizootic were obtained, correlated, and analyzed. A source-receptor model, based on wind direction and speed data, was used to determine whether weather conditions in the Greensburg area enhanced the potential for aerosol spread of pseudorabies virus between herds. On the basis of lack of other modes of spread of pseudorabies and on meteorologic and source-receptor data, aerosol transmission of pseudorabies virus between the 10 herds was probable.     

Associations between genetics, farm characteristics and clinical disease in field outbreaks of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is a disease of domestic swine characterized by exceptionally high clinical variability. This study addresses the question of whether clinical variability in PRRS results from (a) genetic variation among viral isolates and/or (b) variation in management practices among farms on which isolates are found. Genetic data (open reading frame 5 gene sequences) and data on farm characteristics and associated clinical disease signs were collected for 62 PRRS virus (PRRSV) field isolates, representing 52 farms. Clinical disease signs were interrelated — confirming that a true reproductive syndrome exists (involving abortions, infertility in sows, deaths of sows and preweaning mortality).

Pairs of farms experiencing deaths in their sow populations also tended to share viral isolates which were more similar to one another than expected by chance alone. This implies that sow death (one of the more-severe manifestations of PRRS) is under genetic influence. Large herd size was a significant risk factor for the death of sows and for respiratory disease in nursery pigs. All-in–all-out management practices in the nursery were protective against reproductive signs in the sow herd. All-in–all-out management practices in the finishing stages of production were protective against respiratory disease in nursery pigs — but were paradoxically associated with an increased risk of infertility in sows. These results suggest that farm-management practices can also influence which PRRS clinical signs are manifested during an outbreak. In general, signs associated with PRRS appear to result from a combination of genetic factors and herd-management characteristics. The relative contributions of these two influences differ depending on the specific clinical sign in question.     

Herd factors affecting the selection and success of intervention strategies in the program for eradication of pseudorabies (Aujeszky's disease) virus from Illinois swine farms

The program for eradication of pseudorabies virus (PrV) from swine herds in Illinois was evaluated with respect to compliance with Livestock Conservation Institute (LCI) guidelines for selection of intervention strategies and for the effectiveness of these interventions under different herd conditions. The sample consisted of 395 swine operations quarantined between 1988 and 1994. These herds were followed until the end of 1996. The association of herd characteristics (number of sows, sow PrV seroprevalence, type of housing, number of PrV-seropositive farms within 1.5 mi) at the time of quarantine with the producer's selection of an initial intervention strategy (vaccination, offspring segregation, test-and-removal, depopulation-and-repopulation) was analyzed using logistic multiple regression. The interaction of herd characteristics with intervention strategies to affect the duration of quarantine was analyzed using multivariable Cox regression.

Factors favoring selection of vaccination were increased herd size, higher sow PrV seroprevalence, and more PrV-seropositive farms within 1.5 mi. Offspring segregation was preferred when sow PrV seroprevalence was higher, and test-and-removal was preferred when seroprevalence was lower. Depopulation-and-repopulation was more likely in outdoor operations. Except for depopulation-and-repopulation, selection of an intervention strategy was in accordance with LCI guidelines.

Vaccination and offspring segregation were associated with longer times under quarantine, and test-and-removal and depopulation-and-repopulation with shorter times. Test-and-removal was more effective in reducing the duration of quarantine when sow PrV seroprevalence was low. Vaccination increased the duration of quarantine less when sow PrV seroprevalence was high. Vaccination increased the duration of quarantine more when there were one or more PrV-seropositive farms within 1.5 mi than when there were no PrV-seropositive farms within 1.5 mi. It is apparent that herd characteristics affect the duration of quarantine and therefore need to be taken into account in the selection of a PrV-intervention strategy.     

Influence of isoprinosine on lymphocyte function in virus-infected feeder pigs

Pseudorabies is a porcine herpesvirus of major importance in the swine industry. Isoprinosine is an immunomodulating drug that has been shown to be beneficial in treating herpesvirus infections. Twenty-four 7-week-old pigs were allotted within litters to 1 of 4 groups: control, isoprinosine (ISO), pseudorabies virus (PRV), or isoprinosine and pseudorabies virus (ISO-PRV). Isoprinosine was administered daily for 16 days to the ISO and ISO-PRV groups (75 mg/kg of body weight/day, PO). Immunity in pigs in the PRV and ISO-PRV groups was challenged with pseudorabies virus (10(5) TCID50 units) on day 4. Rectal temperatures and viral excretion were monitored daily; total and differential leukocyte counts, lymphocyte response to mitogens, and interleukin-2 production were monitored every 4 days. Pigs challenge-inoculated with pseudorabies virus became ill, with the ISO-PRV group most severely affected. Rectal temperatures were high (P less than 0.05) in virally challenged pigs on days 5 to 12 and 14 to 16; isoprinosine did not alter this effect. Pseudorabies virus-infected pigs had leukocytosis (P less than 0.05) on days 12 and 16, primarily caused by neutrophilia. Concanavalin A-stimulated lymphocyte proliferation was decreased (P less than 0.06) in both PRV and ISO-PRV groups on day 12, compared with control pigs, but only in the PRV group on day 16. Pokeweed mitogen-stimulated lymphocyte proliferation was decreased (P less than 0.02) in ISO-PRV pigs on day 8 of the experiment. Interleukin-2 concentrations, pooled over all sampling days, were decreased (P less than 0.03) in pseudorabies virus-infected pigs. Viral excretion was not altered by isoprinosine treatment. These data suggest that pseudorabies virus infection decreased lymphocyte proliferative responses and interleukin-2 production in pigs, and that isoprinosine did not mitigate these effects.     

Simulation of the economic impact of transmissible gastroenteritis on commercial pig production in Australia

A simulation model (AUSPIG) was used to predict the effect of an increase in piglet deaths, and a reduction in growth rate and an increase in feed conversion ratio of grower pigs on the profitability of two herds representative of the Australian pig industry caused by the introduction of transmissible gastroenteritis virus (TGE) into those herds. For each herd, mortality rates for piglets under 1 week of age of 50% and 95% were assumed to represent a 'moderate' and a 'severe' outbreak, respectively. A reduction in net revenue of 70% was predicted to occur in the 6 months after a 'moderate' outbreak of TGE (100% for a 'severe' outbreak). This represents a total loss of between $260 and $330 per breeding sow in the 12 months after infection with the TGE virus. The likely financial impact of an outbreak of TGE on an Australian piggery is substantial and should be considered when addressing quarantine issues.     

Factors associated with the seroprevalence of pseudorabies virus in breeding swine from quarantined herds.

Strategies for the elimination of pseudorabies virus (PRV) from swine herds include test and removal, offspring segregation, and depopulation/repopulation. The prevalence of PRV in a herd is a major factor in selection of the most appropriate strategy. The purpose of the study reported here was to describe the prevalence of PRV in adult swine in PRV quarantined herds in Minnesota, and to determine herd factors associated with the seroprevalence. Questionnaires describing the health history of the herd, management practices, and design of the swine facilities were obtained from the owners of 142 quarantined herds. Blood was collected from 29 finishing pigs over the age of 4 months, up to 29 adult females, and all herd boars. Factors considered to be significant in a bivariate analysis were combined in a stepwise multiple logistic regression analysis. The prevalence of PRV-seropositive adults in each herd was bimodally distributed among the 142 herds. In 42 (30%) of the herds, none of the females tested was seropositive, which represented the lower mode. At least 90% of the adults tested were seropositive in 30 (21%) of the herds and represented the higher mode. The odds of the breeding swine of a given herd having a PRV seroprevalence of greater than or equal to 20% as compared with having a seroprevalence of less than 20% was 1.654 times higher per 50 adults in the herd, 13.550 times higher if the finishing pigs were seropositive, 2.378 times higher if sows were housed inside during gestation, and 1.481 times lower per number of years since the imposition of quarantine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pathologic consequences of a severe influenza outbreak (swine virus A/H1N1) under natural conditions in the non-immune sow at the beginning of pregnancy

Pathological consequences of a severe outbreak of swine influenza (H1N1 virus) in the non immune sow at the beginning of pregnancy, under natural conditions. A sudden acute outbreak of fever, depression, anorexia and coughing in a group of nulliparous sows from a herd that was currently under epidemiological investigation lead to build a particular disposal of observation. The clinical signs were daily recorded including rectal temperature. Blood was taken from the sows at the beginning of the troubles and 3 weeks later for the detection of Aujesky's disease, coronavirus TGE-like, Influenza viruses A/H1N1 and A/H3N2 and Mycoplasma hyopneumoniae. Viral detection was attempted from nasal swabs and aborted fetuses during the acute phase. The clinical study showed fever reaching near 41 degrees C on most of the pigs and lasting usually from 2 to 5 days. The diagnosis of Influenza (virus swine H1N1) was established both on serology (massive seroconversion) and on the detection of the virus from the nasal swabs and from an aborted fetus. The control of the lungs of sows "not in pig" and culled showed extended lesions of bronchopneumonia and Pasteurella multocida was found. The technical consequences of this severe outbreak of Influenza on reproduction were mainly important at the beginning of pregnancy. Over 13 sows inseminated less than 1 week before the outbreak, only 3 farrowed (respectively 5.5 and 12 piglets); 7 returned to oestrus and 3 "not a pig" at 21 days (echotomography) did not show signs of heat and were culled. Over 8 pregnant sows (1 month of pregnancy), 6 farrowed normal litters and total embryonic resorption occurred in 2 sows. Over 18 pregnant sows (more than 45 days gestation) one aborted.     

Economic assessment of a pseudorabies epizootic, breeding herd removal/repopulation, and downtime in a commercial swine herd

The effect of pseudorabies in a 150-sow farrow-to-finish operation on selected production and economic values was estimated. Mean litter size remained the same throughout the observation period; however, there was a 2-fold increase in suckling pig mortality and a 3.5-fold increase in stillbirths when the months of the epizootic were compared with pre-epizootic months. Following the epizootic, suckling pig mortality was 13.7% greater (P less than 0.05) than that observed in the months preceding the epizootic, whereas stillbirth rate was 71% higher (P less than 0.01) than that reported in the pre-epizootic months. Total net loss for this operation was estimated at +48,175. The major economic losses (approximately 88% of the total loss) were related to breeding herd removal/repopulation and production downtime.     

广西某集约化猪场猪伪狂犬病的监测及净化

为了解某集约化猪场伪狂犬病病毒（PRV）的感染情况,清除感染猪只,净化伪狂犬病,提高猪群的健康水平.采用PRV gE抗体ELISA检测试剂盒,对该场免疫了猪伪狂犬病基因缺失疫苗的猪群进行3次野毒感染检测;应用荧光PCR方法,对临床发病的仔猪进行PRV病原检测.经过动态监测、加强综合防控和逐步淘汰措施,该猪场的PRV野毒感染率从35.29％逐步降低至0％,猪场自繁的仔猪存活率高,无PRV感染,净化效果良好.     

Isolation of a cytopathic virus from weak pigs on farms with a history of swine infertility and respiratory syndrome.

Severe clinical signs of swine infertility and respiratory syndrome (SIRS) of unknown cause were observed in several Minnesota swine farms between November 1990 and March 1991. Forty-five lung samples of weak pigs were collected from 13 swine farms, and virus isolation was attempted using swine alveolar macrophage (SAM) cultures. A cytopathic virus was isolated from 19 lung samples collected from 6 different farms. Four pregnant sows were infected intranasally with a tissue suspension from which virus was isolated, and 4 6-week-old pigs and 2 contact pigs were infected intranasally with 1 of the isolates. The 4 sows farrowed 12 stillborn and 32 normal pigs. Virus was recovered from 10 of 19 pigs examined. Infected 6-week-old pigs were clinically normal except for slightly elevated rectal temperatures and mild respiratory signs. No or mild interstitial pneumonic lesions were observed in inoculated pigs, but the lesion was obvious in the 2 contact pigs. Seroconversion was observed in sows and pigs as measured by indirect fluorescent antibody (IFA). Serologic identification of the isolates was carried out by IFA using reference serum prepared from an experimentally infected sow. A cytoplasmic fluorescence was observed on the SAM monolayers infected with each of the 19 different isolates. Fluorescence was also observed when the monolayers were tested with SIRS virus ATCC VR-2332-infected sow sera. Replication of the isolates was not affected in the medium containing 5-iodo-2'-deoxyuridine but was inhibited by treatment with ether. The isolates were relatively stable at 56 C and did not agglutinate with various erythrocytes tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of pseudorabies virus-infected swine herds by evaluating the serostatus of boars or finishing pigs

Data were collected from 39 Minnesota swine farms quarantined for pseudorabies virus (PRV) infection. Each herd was serologically evaluated for antibodies to PRV in the sows, boars, and finishing pigs. To identify PRV-seropositive swine herds, the Kappa statistic was used to estimate the effectiveness of evaluating the PRV serostatus of boars or of finishing pigs. Using the serostatus of all herd boars, the sensitivity (with 95% confidence interval) of identifying PRV-infected herds was 58 +/- 22%, and the specificity was 100 +/- 0%; Kappa statistic was 0.55. Using the serostatus of a representative sample of finishing pigs, the sensitivity of identifying PRV-infected herds (with 95% confidence interval) was 63 +/- 22%, and specificity was 87 +/- 23%; Kappa statistic was 0.40. The PRV serostatus of herd boars or of a representative sample of finishing pigs did not accurately reflect the PRV serostatus of the herd.     

A seroepizootiologic study of five viruses in a swine-evaluation station.

This serologic study was done to gain information on the spread, maintenance, and effect upon performance of five porcine viruses. Blood samples were taken from two groups of 8- to 11-week-old pigs from a large number of Indiana swine herds in a performance-testing station 1 week after entry, 7 weeks after entry (one group only), and at slaughter. The sera were tested by indirect fluorescent antibody tests for antibodies to transmissible gastroenteritis virus (TGEV), swine influenza virus (SIV), hemagglutinating encephalomyelitis virus (HEV), porcine adenovirus (PAV), and pseudorabies virus (PRV). Seroconversions to TGEV, HEV, and PAV occurred in a group of pigs entered in May and slaughtered in August (group 1). In the group that was entered in October and slaughtered in January (group 2), pigs developed antibodies to SIV, HEV, and PAV, but not to TGEV. Only 1 of the 434 pigs tested had antibodies to PRV, and there were no seroconversions to this virus. The only statistically valid effect of infection on performance was found in group 1 pigs, which had seroconverted to TGEV during the first 7 weeks of their stay. These pigs gained 0.077 kg less per day than pigs that did not develop antibodies to TGEV during that period. The pattern of serologic reactions was indicative of a relatively slow spread of these viruses in the groups. We interpret this as supporting the concept that a relatively slow spread of these viruses through large groups of pigs kept under conditions that are less than optimum for virus spread may be an important means of their interepizootic survival.